Heretofore, liquid crystal display devices performing reflective display have been increasingly in demand. This type of liquid crystal display device has a structure in which outside light, such as natural light and indoor illumination incident from the front side (observer side) is reflected at a reflective layer, whereby reflective display is performed. According to this structure, since no backlight is required, reflective display has advantages in that low electric power consumption and reduction in weight can be achieved. As a result, reflective liquid crystal display devices, typically represented by portable electronic apparatuses or the like, are widely used.
FIG. 11 is a cross-sectional view showing an example of the structure of a conventional reflective liquid crystal display device. In this figure, a passive matrix liquid crystal display device 5A is shown by way of example. As shown in this figure, the liquid crystal display device 5A has a structure in which a backside substrate 51 and a front substrate 52 are bonded together by a sealing material 53 in the form of a frame. Liquid crystal 54 is enclosed between the substrates. In addition, on the surface of the front substrate 52 at the liquid crystal 54 side, a plurality of transparent electrodes 521 extending in a predetermined direction is formed. Furthermore, the surface of the front substrate 52 having the transparent electrodes 521 formed thereon is covered with an alignment film 522. Rubbing treatment is performed on the alignment film 522 to define an alignment direction of the liquid crystal 54 when no voltage is applied thereto.
In addition, on the surface of the backside substrate 51 at the liquid crystal 54 side, a reflective layer 511, an insulating layer 512, a color filter layer 513, and a protective layer 514 are formed in this order. The reflective layer 511 is a thin-film composed of a metal (e.g., aluminum) having reflective characteristics. The insulating layer 512 is a thin-film for protecting the reflective layer 511. The color filter layer 513 is composed of a plurality of color pixels 513a and a shading layer (black matrix) 513b. 
The protective layer 514 is a thin-film for protecting the color filter layer 513. On the surface of the protective layer 514, a plurality of transparent electrodes 515 is formed extending in the direction perpendicular to the transparent electrodes 521. The surface of the protective layer 514 having the transparent electrodes 515 formed thereon is covered with an alignment film 516 similar to the alignment film 522.
Furthermore, between the alignment film 516 at the backside substrate 51 side and the alignment film 522 at the front substrate 52 side, a plurality of spheric spacers 55 is dispersed. These spacers 55 are used for uniformly maintaining the distance (hereinafter referred to as “cell gap”) between the backside substrate 51 and the front substrate 52.
In the structure described above, after light incident from the front substrate 52 side is transmitted through the front substrate 52 and the liquid crystal 54, the light is reflected at the reflective layer 511. The light thus reflected is again transmitted through the liquid crystal 54 and the front substrate 52 and is then emitted to the observer side. As a result, reflective display is performed.
The surface of the reflective layer 511 is a specular surface. Accordingly, as shown in FIG. 12, strong light (regular reflection light) is emitted in the direction H perpendicular to the surface of the substrate of the liquid crystal display device 5A. However, as an angle θ shown in FIG. 12 is increased, the intensity of the emitted light is decreased. As a result, at a position at which the angle θ is large, a problem may arise in that the displayed image is darkened.
In order to solve the problem described above, an external scattering liquid crystal display device is proposed. FIG. 13 is a cross-sectional view showing an example of the structure of this type of liquid crystal display device. In this connection, the same reference numerals of the elements in FIG. 11 designate the corresponding elements in FIG. 13, and descriptions therefor are omitted. As shown in FIG. 13, a liquid crystal display device 5B has a diffusion filter 56 at the outside of the front substrate 52.
In the liquid crystal display device 5B, after light incident from a front substrate 52 side is scattered by the diffusion filter 56, the light thus scattered is transmitted through the front substrate 52 and liquid crystal 54 and is then reflected at a reflective layer 511. After the light thus reflected is again transmitted through the liquid crystal 54 and the front substrate 52 and is then scattered by the diffusion filter 56, the light is emitted to an observer side. As described above, according to the liquid crystal display device 5B employing the external scattering method, in addition to the regular reflection light, the light scattered by the diffusion filter 56 can also be used. Accordingly, compared to the liquid crystal display device 5A only using the regular reflection light, strong light can be emitted to a broader area. As a result, bright display can be performed in a broader area.
However, in the liquid crystal display device 5B, while light enters the liquid crystal display device 5B and is then emitted to the observer side, light observed by the observer is scattered twice by the diffusion filter 56. Accordingly, a problem may arise in that the outline of the display image is blurred.
In order to solve the problem described above, an internal scattering liquid crystal display device is proposed. FIG. 14 is a cross-sectional view showing an example of the structure of this type of liquid crystal display device. In this connection, the same reference numerals of the elements shown in FIG. 11 designate the corresponding elements in FIG. 14, and descriptions therefor are omitted.
As shown in FIG. 14, in an internal scattering liquid crystal display device 5C, the surface of a backside substrate 51 at a liquid crystal 54 side is roughened. That is, a plurality of minute protrusions and a plurality of minute recesses are formed on the surface described above. A reflective layer 517 is formed on this roughened surface. Accordingly, on the surface of the reflective layer 517, protrusions and recesses are formed in conformity with the protrusions and recesses formed on the surface of the roughened surface.
In this liquid crystal display device 5C, after light incident from a front substrate 52 side is transmitted through a front substrate 52 and liquid crystal 54, the light is reflected at the surface of the reflective layer 517. As described above, the minute protrusions and the recesses are formed on the surface of the reflective layer 517. Accordingly, after the light reaching the reflective layer 517 is reflected in a appropriately scattered state, the light is again transmitted through the liquid crystal 54 and the front substrate 52 and is then emitted to an observer side. According to the structure described above, in addition to the regular reflection light, the scattered light can also be used, and hence, compared to the liquid crystal display device 5A only using the regular reflection light, strong light can be emitted to a broader area. As a result, high quality display can be preformed in a broader area. In addition, in the liquid crystal display device 5C, the light is scattered once. As a result, compared to the external scattering liquid crystal display device 5B, blurring along the outline of the display image can be suppressed.
In addition, a transflective liquid crystal display device employing the internal scattering method is also proposed. FIG. 15 is a cross-sectional view showing an example of the structure of this type of liquid crystal display device. In this connection, the same reference numerals of the elements in FIG. 11 or 14 designate the corresponding elements in FIG. 15, and descriptions therefor are omitted.
As shown in FIG. 15, a liquid crystal display device 5D is provided with a backlight unit 57 under a backside substrate 51. The backlight unit 57 contains a light source 571 and a light guide plate 572. The light source 571 is, for example, a cold cathode tube. The light guide plate 572 guides light incident on a side edge surface thereof, which is emitted from the light source 571, to the backside substrate 51 side. In addition, in the liquid crystal display device 5D, instead of the reflective layer 517 of the liquid crystal display device 5C described above, a transflective layer 519 is provided. The transflective layer 519 is a thin-film composed of aluminum or the like having a plurality of aperture portions 519a therein.
In the structure described above, light incident from a front substrate 52 side is transmitted through the front substrate 52 and liquid crystal 54 and is then reflected at the surface of the transflective layer 519. The light thus reflected is again transmitted through the liquid crystal 54 and the front substrate 52 and is then emitted to an observer side. As a result, a reflective display is performed.
In addition, in a dark place, the light source 571 is turned on, and transmissive display is performed. That is, light emitted from the light source 571 is guided to the backside substrate 51 side by the light guide plate 572. This light is transmitted through the backside substrate 51, the aperture portions 519a in the transflective layer 519, the liquid crystal 54, and the front substrate 52 and is then emitted to the observer side. As a result, transmissive display is performed.
In the liquid crystal display device 5C or 5D employing the internal scattering method, as shown in FIG. 14 or 15, a case is supposed in which the entire surface of the backside substrate 51 is roughened. In the case described above, a sealing material 53 is formed on the roughened surface. However, when this structure is employed, the adhesion between the sealing material 53 and the backside substrate 51 is degraded, and hence, a problem may arise in that the strength of the sealing material 53 is partly degraded. In addition, since the adhesion between the sealing material 53 and the surface of the backside substrate 51 is degraded, a gap may be formed therebetween in some cases. Furthermore, the gap thus formed may extend from an area (that is, an area formed between the backside substrate 51 and the front substrate 52 opposing thereto) at which the liquid crystal 54 is enclosed to the outside in some cases. When the gap described above is formed, a part of the enclosed liquid crystal 54 may leak outside via the gap, or the liquid crystal 54 may be mixed with water moisture penetrating from the outside into the area via the gap. As a result, a problem may arise in that the display characteristics of the liquid crystal display device are degraded.
In addition, in order to uniformly maintain the cell gap, a proposal is made in which a sealing material 53 containing cylindrical glass fibers therein is used. However, when the sealing material 53 is formed on the roughened surface, some of the glass fibers are placed on the top portions of the protrusions of the roughened surface, some of the glass fibers are placed at the bottoms of the recesses of the roughened surface, and as a result, a problem may arise in that the cell gap cannot be uniformly maintained.
In order to solve the problems described above, it may be considered that a part of the backside substrate 51 is formed to have a flat area at which the sealing material 53 is formed. In the case described above, since the sealing material 53 and the backside substrate 51 can be satisfactory bonded together, the problems described above can be solved. However, when the structure described above is employed, determination of the boundary between the flat area and the roughened area may become a problem.